The first full day of sessions at the 22nd International AIDS Conference (AIDS 2018) in Amsterdam was filled with new scientific findings shared by researchers from around the world. In a Facebook Live interview with HIV.gov, Carl Dieffenbach, Ph.D., discussed highlights of three studies presented today at the conference, including:

an update on a potential association between the HIV treatment medication dolutegravir and birth defects;

additional research on the effectiveness of HIV treatment as prevention among gay male serodifferent couples; and

a study on whether there may be drug-drug interactions between PrEP and feminizing hormone therapy for transgender women.

Birth defects potentially associated with use of dolutegravir at time of conception—Dr. Rebecca Zash of the Botswana-Harvard AIDS Partnership, an NIH-supported study in Botswana evaluating the risk of birth defects among women living with HIV who were taking antiretroviral therapy provided additional information about a previously reported signal from the study. In May, the investigators reported that about 4 in 400 babies born to women who were taking a dolutegravir-based antiretroviral regimen at the time of conception had a neural tube defect—a very high rate of a serious birth defect. Today, Dr. Zash reported that among an additional 170 newborns born to women who were taking dolutegravir at the time of conception, there were no additional neural tube defects. Additional data are needed from the Botswana study and other cohorts to determine the true impact of dolutegravir on birth defects, observed Dr. Dieffenbach. Out of an abundance of caution, the FDA (PDF, 59 KB) and U.S. Department of Health and Human Services have recommended that women living with HIV who desire to become pregnant discuss alternative antiretroviral drug regimens with their health care providers while research continues. They have also recommended that women of childbearing potential who decide to take dolutegravir use effective contraception. Read the study abstract.

Additional evidence of the effectiveness of HIV treatment as prevention among gay male serodifferent couples—Dr. Dieffenbach recounted the important findings first reported today from the PARTNER2 study confirming that “treatment as prevention” is as highly effective among gay, bisexual, and other men who have sex with men as it is among heterosexual couples. Alison Rodger of University College London reported that among nearly 1,000 serodifferent couples followed in the PARTNER2 study, there were zero cases of HIV transmission when the HIV-positive partner was on antiretroviral therapy (ART) and had achieved and was maintaining viral suppression. The study tracked nearly 75,000 condomless sex acts. Dr. Rodger described this as “robust evidence that the risk of HIV transmission [when the HIV-positive partner is virally suppressed] is effectively zero.” Dr. Dieffenbach concurs, observing that these findings finally “nail shut” the question of whether there’s enough evidence to support the idea that undetectable=untransmittable (U=U) for gay men, too. (Read more about U=U in the recent blog from NIAID.) The findings reinforce that once an HIV-positive person achieves and then maintains viral suppression, there is effectively no risk of transmitting HIV to their HIV-negative partners. That information, he emphasized, needs to get out to people living with HIV, their partners, and healthcare providers. View the abstract.

PrEP has no impact on feminizing hormone therapy—Finally, Dr. Dieffenbach discussed research findings presented today that help address a concern among many transgender women about whether or not to use HIV pre-exposure prophylaxis (PrEP). Concerns about putative drug-drug interactions between PrEP and feminizing hormone therapy potentially may lead some transgender women to prioritize taking the hormones over PrEP. First, Dr. Dieffenbach defined a drug-drug interaction. Then he discussed findings presented at AIDS 2018 today by Akarin Hiransuthikul of the Thai Red Cross. Dr. Hiransuthikul reported that he and fellow researchers found no impact of tenofovir, one of the two drugs in PrEP, on the level of feminizing hormone in the body. The researchers identified a slight reduction in the level of tenofovir that they observed merits further study to determine if this reduction is clinically significant. Dr. Dieffenbach reported that this important finding may alleviate the concern for transgender women about a drug-drug interaction between feminizing hormone therapy and PrEP. Read the study abstract; view the presentation (PPT, 306 KB).

The Conference

The 22nd International AIDS Conference is taking place this week in Amsterdam. It has gathered over 15,000 HIV researchers, public health experts, policy makers and members of the HIV affected community from 160 nations to share and discuss the latest HIV science and innovations in prevention and treatment.

More Updates to Follow from HIV.gov

As the conference continues this week, we will bring you additional interviews with representatives of CDC's domestic and global HIV programs, HRSA's HIV/AIDS Bureau, USAID, and PEPFAR, as well as more daily HIV research highlights Dr. Dieffenbach. Review this post for HIV.gov’s schedule and follow us on Facebook and Twitter for details.

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